Microsoft has blacklisted a subordinate CA certificate that was wrongfully used to issue SSL certificates for several Google websites. The action will prevent those certificates from being used in Google website spoofing attacks against Internet Explorer users.

Microsoft’s move, taken on Tuesday, came after Google reported that the China Internet Network Information Center (CNNIC), a certificate authority (CA) trusted by most browsers and operating systems, issued an intermediate certificate to an Egyptian company called MCS Holdings. The company then used it to generate SSL certificates for Google-owned websites without authorization.